Startling A Spider
Jumping spiders, a favorite of ours around this time of this year on the occasion of Halloween, were thought to be primarily visual creatures. And why would they not be? These spiders have four pairs of eyes giving them near 360-degree vision and even the ability to see ultraviolet light, some say. A recent, and accidental, discovery now tells us that these animals can also hear airborne sounds from as far away as 10 feet.
Scientists at Cornell were recording brain responses to visual stimuli in the laboratory when one of them casually moved a chair in the lab. It took everyone by surprise when the spider’s brain responded to the sound. Spiders do not have tympanic ears and hence should not be able to hear airborne sounds from afar. What ensued was first the most casual of experiments by clapping to the spider from various distances. Indeed, the spider could hear.
To fully understand the phenomenon, these scientists then recorded behavioral and neural responses to various sounds in an anechoic chamber. The spider showed an acoustic startle response by freezing when presented with sound. The scientists also verified neural activity in response to these sounds. It turned out that these spiders are most sensitive to sounds between 80 and 130 Hz, the approximate frequency range of sound created by the wing beat of their primary predator, a particular group of wasps.
So the final piece of the puzzle was to figure out how the spider could hear the airborne sound without having a traditional ear. It turns out these spiders have specialized hair on their legs. Sound causes these hairs to vibrate, which are connected to a neural system that triggers activity in the hearing center of the spider’s brain.
There you have it, a super spider with eight eyes and hair that can hear. Watch out for these guys when you are out trick or treating this Halloween.
Shamble P, Menda G, Golden J, Nitzany E, Walden K, Beatus T, Elias D, Cohen I, Miles R, Hoy R. (2016) Airborne Acoustic Perception by a Jumping Spider. Current Biology October.